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A new report has pointed to a bleak future for many of the world’s killer whales (orcas). In fact, it says that at least half of the world’s population are likely to become extinct because polychlorinated biphenyls (PCBs) are still leaking into the world’s oceans, despite having been banned by the US in 1978 and the Stockholm Convention on Persistent Organic Pollutants in 2001.

PCBs were widely used from the 1930s onwards in electrical coolants and insulators, carbonless copy paper etc., but we have known for around 50 years that they are toxic. Around 800,000 tonnes of PCBs still exist and are supposed to be being destroyed, but the work is well behind schedule. As a result, PCBs are still leaking from landfills and other sources into the sea. Once in water, PCBs don’t dissolve, gradually sinking and becoming more and more concentrated in deep water.

PCBs are known to cause a range of illnesses including liver damage and cancer in humans and can also affect fertility. When animals eat small amounts of PCBs, they can suffer changes to their immune systems, behaviour changes and reduced fertility. Higher doses cause liver damage and death.

This new research has found that in areas of ocean where PCBs are present in relatively large quantities, killer whales are showing extremely high levels of PCBs in their bodies; sometimes up to 100 times the safe limit. As top predators, orcas eat large quantities of contaminated fish. Not only are the PCBs causing harm to adult whales and affecting their ability to reproduce, they are also being passed in mothers’ milk to their young, poisoning calves.

Among the orca populations most at risk is the last group or ‘pod’ to live off the coast of the UK. Levels of PCBs found in a dead killer whale from the UK population were among the highest ever recorded. More orcas are in danger in the waters off Gibraltar in the Mediterranean, the north-east Pacific, Japan, and Brazill. The report predicts that they could vanish from these waters within the next 50 years.

There is some cause for hope though. Killer whales living in northern oceans around Iceland, Canada and Norway are much less contaminated, as they are further away from the sources of the PCBs still leaking into our seas. For the moment at least, it seems the Arctic orcas are safe from the threat of PCBs.